mthompson1951

Have this car which is Dad's last Olds. Going to do a full tune up and replace a bunch of things. Have had Split Fire plugs in it for a while, but no longer available.

Chiltons lists @10 different brand plugs for this year. I've been told by an '83 owner that he got best performance and mileage with AC Delco's.

Anybody know what is the best performance plug for power & mileage for this car? Need an answer soon. Going in tomorrow.

Allan R

X2 on AC Delco
That's what I used in my 83 Ninety Eight and never had any issues. Just make sure you set the plug gap properly and have good spark plug wires. The wires shielding and resistance does change over time.

One mech I talked with recommended using only the AC Delco Copper core. They worked very well.

EDIT: Your gap should be around .060 IIRC. On older engines I sometimes will change this down to .050

ah64pilot

I have always run NGK plugs and have ALWAYS been happy with them. And Allan, I think you're crazy...0.060"! I gap mine at 0.045", stock is 0.030"

I'm not familiar with the 307 but .060" seems like a lot for anything. Where did you get that number? Is it in the manual or something?

FAZ442

Yes .060 is quite a bit.... I would do no more than .035 on this car

Allan R

Yup, I used that based on the 83 CSM which was 2 volumes for that year. Got them when I bought my 83 Regency Brougham. I never checked the owners manual - just the CSM. The factory gap specifies .060 I know it sounds like a lot. If you check the early HEIs from 75 -80? I believe they gapped at .050

FWIW, I've tried all kinds of spark plugs. Maybe some engines just seem to get along better with some brands and not others? I had NGK in my 95 Regency and it didn't like them. Changed to Champion copper cores and it LOVED them.

Have a look at this: https://classicoldsmobile.com/forums...s-307-gap.html

Not crazy guys, just going from what I remember on my 307. Ran it from 83-2003. Always started and ran smooth. A bit of a slug on the highway for high speed passing with that whopping 140 hp, but decent driver coupled with a 200R4.

Only part of it that let me down ever was the water pump - right in the middle of winter too. Had to work fast to git'r done while the block was still warm.

My 72 I gap at .040 just like you guys. If I don't like the way it runs I'll drop it down to .035 too.

ThePackRat

Some of the 1st HEI cars actually called for gaps of .080



They later bumped the spec back down to .060

When it doubt stick with .060 ... but I'd never go with .080

I've done .045 myself with no ill effects.

Redog

My experience, stock ACDelco's is all a GM car likes

coppercutlass

The 307 i have now in the 72 runs well with the champion plugs gapped to .045 . I see spark plus as one of those things i should not worry about untill you are really making some serious hp or certain weathers. I just run a good name brand plug that has never failed me . I ran the same plugs in my 350 before w/no issues.

tcturner

1985 delta 88 owners manual but i use the ac 41 630 plugs in mine<br/>

olds 307 and 403

The AC Delco's are OK but not as good the old ones. I find the NGK XR 45 actually run smoother in low compression Olds V8's gapped at .045" or .050".

76olds

X2 NGK XR 45 .045 gap on my 350, but this thread is over 4 years old. It may help some new members though.